Cloaking is a black hat search engine optimization (SEO) technique in which the content presente to the search engine spider is different to that presented to the users' browser. This is done by delivering content based on the IP addresses or the User-Agent HTTP header of the user requesting the page. When a user is identified as a search engine spider, a server-side script delivers a different version of the web page, one that contains content not present on the visible page. The purpose of cloaking is to deceive search engines so they display the page when it would not otherwise be displayed.